How do analog and digital signals work in the context of physics or electricity?

Traditionally, internet is accessible to every home via the normal telephone lines connected. The data transmitted from the telecommunication company (also ISP) to a DSL modem inside each home is in form of analog (voice) signal. Then, the modem converts the analog signal to digital signal and sends it to a connected computer.

The digital signal is represented by the number zero (0) and one (1). But physically, it's a voltage pulse. For example, if the modem detects the voltage pulse from within the cable greater than zero, it interprets as 1; otherwise, it interprets as 0.

The analog signal is pictured as a wave signal. But physically, it's just a series of voltage pulses within a timeframe. The voltage generated within the cable continuously rises and drops again and again within a time interval so that the signal receiving device can conceptually interpret it as wave frequency.

Reference:

https://www.computernetworkingnotes.com/networking-tutorials/how-analog-and-digital-signals-work.html

Setting up Wireless Access Point using Apple's Airport Express

I'm using ADSL internet connection at my home, in which there is a cable from ISP connected directly into my modem. I want to set up a wifi network from it. The only thing I need is Airport Express. I just plugged in the ethernet cable from the modem to the Airport Express and configure it as following:

1. Connecting modem to Airport Express

2. Configuring the Airport Express from MacBook/iPhone/iPad by using Airport Utility application. The application come with Mac OS X by default. You need to download and install the app for iPhone and iPad. The steps below show how to configure it.